Process for producing errosion and wear resistant metal composites

ABSTRACT

Erosion and wear resistant metal composites are disclosed that comprise a metal alloy substrate and a coating composition bonded to said substrate; the coating composition consisting essentially of nickel, chromium, boron, silicon and titanium carbide in the following percentages by weight of the coating composition: NICKEL14% TO 80% CHROMIUM0.5% TO 10% BORON0.2% TO 5% SILICON0.3% TO 8% TITANIUM CARBIDE 6% TO 82% A process is disclosed for producing the composites wherein a first coating containing all of the foregoing metals are applied via a slurry coating technique followed by drying, heating and pressing steps and thereafter a second slurry coating step is used wherein the metal ingredients of nickel, chromium, boron and silicon are applied followed by drying and heating steps.

nited States Patent 1191 Reznik [451 Aug. 28, 1973 PROCESS FOR PRODUCING ERROSION AND WEAR RESISTANT METAL COMPOSITES [75] Inventor: Barry David Reznik, Brooklyn, NY.

[73] Assignee: DeWiant Corporation, Detroit,

Mich.

221 Filed: Sept. 10,1971

21 Appl. No.: 179,538

Related US. Application Data [62] Division of Ser. No. 828,702, May 28, 1969.

803,649 l0/l958 Great Britain ll7/7l M Primary Examiner-Alfred L. Leavitt Assistant Examiner-J. R. Batten, Jr. Attorney-Norman J. OMalley et a1.

[ ABSTRACT Erosion and wear resistant metal composites are disclosed that comprise a metal alloy substrate and a coating composition bonded to said substrate; the coating composition consisting essentially of nickel, chromium, boron, silicon and titanium carbide in the following percentages by weight of the coating composition:

nickel 14% to 80% chromium 0.5% to 10% boron 0.2% to 5% silicon 0.3% to 8% titanium carbide 6% to 82% A process is disclosed for producing the composites wherein a first coating containing all of the foregoing metals are applied via a slurry coating technique followed by drying, heating and pressing steps and thereafter a second slurry coating step is used wherein the metal ingredients of nickel, chromium, boron and silicon are applied followed by drying and heating steps.

4 Claims, No Drawings PROCESS FOR PRODUCING ERROSION AND WEAR RESISTANT METAL COMPOSITES CROSS REFERENCE TO RELATED APPLICATION This application is a divisional application of Ser. No. 828,702, filed May 28, 1969, which is assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION This invention relates to erosion and wear resistant metal composites. More specifically it relates to metal composites that are particularly well suited for the fabrication of compressor blades and other jet engine parts that are subjected to erosion and wear by solids, generally in the form of dust. As is known, the replacement costs resulting from dust erosion of military and commercial gas turbine engines are excessive.

Erosion resistant parts fabricated from alloys such as 41088, AM350 and IN718 can be made by providing.

a coating composition over the alloy substrate via the chemical vapor deposition of titanium carbidc. Although this process provides parts having excellent erosion resistance, it is a difficult and costly process.

It is also known that the erison resistance of various materials depend upon several factors, among erosion are the physical characteristics of the material and the angle of impact of the solids. For example, maximum erosion of ductile materials occurs when the impact angle is about 20 and for brittle materials an impact angle of about 90 causes the maximum erosion.

It is believed, therefore, that a composite that will resist erosion regardless of the angle of impact of the solids and is relatively easy to produce with excellent reproducibility would be an advancement in the art.

SUMMARY OF THE INVENTION In accordance with one aspect of this invention, there is provided a metal composite comprising an alloy sub strate, as a major component and bonded to the substrate an erosion resistant coating composition consisting essentially of the following materials in percentages by weight:

nickel 14% to 80% chromium 0.5% to 10% boron 0.2% to 5% silicon 0.3% to 8% titanium carbide 6% to 82% In accordance with another aspect of this invention, there is provided a process for producing said metal composite. The process comprises (a) applying to a clean alloy substrate a first coating of a slurry comprising a powdered metal material, a fugitive binder and a fugitive solvent for the binder; the powdered metal material consisting essentially of the following ingredients in percentages by weight of the total metal material:

nickel 6.5% to 30% chromium 0.5% to 3.5% boron 0.2% to 2.0% silicon 0.3% to 2.5% titanium carbide 67% to 91% (b) drying the substrate to remove said solvent to form a first coating; (c) heating the substrate having the first coating to a temperature of from about 1,750F to about 1,900F in an inert atmosphere for at least about 10 minutes; ((1) hydrostatically pressing said coated substrate at pressures from about 10,000 psi to about 40,000 psi; (e) applying a second coating of a slurry that comprises a fugitive binder, a fugitive solvent for the binder and a second powdered metal material consisting essentially of the following ingredients in percentages by weight of the total second powdered metal material:

nickel to chromium 4.6% to 11.5% boron 22% to 5.5% silicon 3.2% to 8.0%

and (f) heat treating said substrate containing the first and second coatings under atmospheric conditions and for a time substantially the same as in (0) above and to at least about 1,780F to thereby produce a composite containing an erosion-resistant coating composition having a thickness of from about 3 to about 15 mils.

For a better understanding of the present inventions, together with other and further objects, advantages and capabilitites thereof, reference is made to the following disclosure and appended claims in connection with the above description of some of the aspects of this inven' tron.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, the composites of this invention are produced by use of the slurry technique of applying coatings. The slurries used comprise a powdered metal material, a volatile or fugitive binder and a volatile or fugitive solvent for the binder. These methods are well known in the art and are used for applying metal coatings by spraying, dipping or brushing of the slurry onto the substrate followed by a drying and heating step wherein essentially all of the binder and solvent are removed and the metal'material adheres to the substrate. The types of suitable binders and solvents are known to one. skilled in the art of coating compositions.

The metal powders are thoroughly mixed together in a suitable blender or mixing device (e.g. a V blender) until a substantially homogeneous composition has been obtained. A similar procedure is followed if a mixture of different alloys or of elemental metal (or metalloid) and of alloyed material is employed.

The powdered metal is converted into a liquid coating composition, adapted for application (e.g., by dipping, brushing, spraying or the like) to the superalloy substrate, by suspending it in a suitable vehicle, e.g., a solvent solution of temporary or fugitive binder which can be a natural or synthetic binder.

Examples of fugitive binders that can be employed are solvent solutions or dispersions of the various available synthetic polymers, such as polyacrylamide, polyvinyl acetate and the homopolymers and copolymers of the lower alkyl (e.g., C through C acrylates and methacrylates with each other and with other compounds containing a monoethylenically unsaturated grouping. It is preferred to employ an ordinary nitrocellulose (pyroxylin) lacquer wherein the solvent is, for example, acetone.

The concentration of the powdered metal in the vehicle and the amount of solvent in the same are varied as desired, depending upon such factors such as the particular method of applying the coating (brushing, spraying or dipping), the desired thickness of the individual coating, the number of coatings to be applied, the viscosity of the vehicle, the desired covering power of the coating composition, and other influencing factors. Typically, the metal power is present in he coating composition in an amount corresponding to about 1,500 to about 3,000 grams per 1,000 gms. of the vehicle.

The powders are mixed with the vehicle by mechanical stirring. Any suitable mixer can be used, however, mixers of the type generally employed in mixing paints are preferred for this purpose. Mixing is continued at any suitable temperature for a time sufficient to provide a substantially homogeneous composition. The titanium carbide and the nickel, chromium, silicon and boron are generally incorporated into the slurry in the form of a finely divided powder having essentially all of the particles of the powdered metal smaller than the openings in a 325 mesh screen (U.S. Sieve.). The titanium carbide and the other ingredients can be added to the slurry individually or can be added separately as long as the final slurry has the proper amounts of desired metals relatively uniformly distributed throughout the slurry. Any suitable mixer can be used to provide the relatively uniform slurry such as those normally used for mixing paints.

Although the amount of nickel, chromium, boron and silicon can be varied within the ranges heretofore given, it is preferred to use a nickel base alloy braze consisting essentially of about 86 percent nickel, about 6.5 percent chromium, about 3 percent boron and about 4.5 percent silicon to provide a ductile matrix for the titanium carbide. The weight ratio of the foregoing alloy brazes to the titanium carbide can be varied from about 1:10 to about 1:2 with satisfactory results. A weight ratio of nickel base alloy to titanium carbide of from about 1:4 to about 1:6 is preferred.

After the first slurry coating is applied and thereafter dried, the coated material is heat treated at a temperature of from about 1,750F to about 1,900F for a relatively short period of time, generally less than about one hour. Although the temperature can be varied between about 1,750F and 1,900F and some of the benefits of the invention can be achieved, it is preferred to use a temperature of from about 1,830F to about 1,850F, low temperatures tend to not sufficiently wet the titanium carbide particles and the higher temperatures can have some undesirable effects upon the properties of the substrate particularly if the temperature is maintained near the upper limit for prolonged periods, such as over an hour. Thereafter, the coated material is isostatically pressed to increase the density of the first coating. Generally, the pressures used are from about 10,000 psi to about 40,000 psi. It has been found that pressures of from about 15,000 psi to about 25,000 psi yield densities that are preferred. In order to compact the first coating it is necessary to enclose the coated substrate in a relatively thin film of a relatively impervious material such as a polyethylene plastic film. An example of such a material is Visten film manufactured by Union Carbide Corporation.

After the isostatic pressing step, the coated material is coated with a second slurry. Although in most instances, for ease of operation, a slurry that is essentially the same as the slurry used for the first coating but without the titanium carbide, will be used for the second coating. The second coating can be varied within the specified amounts ofingredients, therefore, the sec ond slurry can contain powdered metal materials in the following ranges:

nickel 75% to 90% chromium 4 6% to 11.5% boron 2.2% to 5.5% silicon 3.2% to 8 0% As can be appreciated, the same or different formulations can be used for the first and second coatings with the exception of the addition of titanium carbide in the first coating and absence thereofin the second coating. However, use of the same formulation is preferred. The second coating infiltrates the relatively porous first coat thus yielding excellent strength and appearance to the coated substrate. After the second coating has been applied the coated substrate is dried and heated to a temperature of from at least about 1,780F to about 1,900F and preferably from about 1,830F to about 1,850F for at least about 10 minutes.

The overall thickness of the coating can be varied. A coating having a thickness at least about 3 mils is needed to provide appreciable resistance to erosion. In general, as the thickness of the coating is increased, the lifetime of the composite is increased. In most instances however, from an economic standpoint and because adherence of large thicknesses of coatings is difficult, the overall thickness of coating greater than about 15 mils will not be used.

It is to be noted that although two separate coating applications are used, there are not two distinct layers. Photomicrographs of a cross section of the metal composite indicates a relatively complete diffusion of the ingredients of the coating and some diffusion between the substrate and the coating. In some instances the titanium carbide particles are relatively more concentrated at the center of the coating and with the nickel alloy matrix being relatively more concentrated at the surface and interface.

The ratio of thickness between the first and second coating applications can be varied. In most instances, the ratio of first coating thickness to second coating thickness will be from about 1:9 to about 9:1 with a range of from about 1:5 to about 5:1 being preferred, In the process of the present invention it is only necessary to vary the weight ratios of the slurry application to achieve the beforementioned ratios.

It is believed that the combination of the ductile and brittle materials that comprise the coating composition of this invention offer the advantages of being resistant to erosion regardless of the angle of impact of the solids. As was previously mentioned, the angle of maximum erosion for ductile materials is about 20, therefore, even though the ductile nickel base alloy erodes at surfaces that are subjected to these angles, the titanium carbide particles being hard and brittle will resist erosion. At higher angles, such as about 90 the nickel alloy matrix will offer its largest resistance where the attack on the brittle titanium carbide is the greatest. The choice of the level of the particular ingredients, that is titanium carbide and nickel alloy, will depend to a large degree upon the particular use and the impact angles of a majority of the paritcles causing the erosion.

Although the metal components of the coating can vary, as well as the thickness of each layer within the limits heretofore given, it is preferred that the overall coating compositions have the following ranges of ingredients in percentages by weight:

nickel 50% to chromium 3% to 7% boron 1% to 3% silicon 2% to 5% titanium carbide 15% to 45% Although cemented carbides are the closest structurally to the type of coatings used for the metal composites of this invention, the processing temperature for producing the cemented carbide coatings is about 3,000F which is above the melting point of many of the alloys that can advantageously be employed in the composites of this invention.

Alloys that can be utilized as substrate in the practice of this invention include stainless steels, nickel or cobalt based superalloys or other alloys thermally stable at the processing temperatures used in the practice of this invention, that is alloys that are thermally stable at temperatures about 1,750F. Other alloys will be suggested to one skilled in the art reading the disclosure contained herein.

When some alloys are used as substrates, the bond of the coatings to the substrate can be even further improved by incorporating relatively small amounts of silver as one of the ingredients of the coating. In most instances, the amount of silver is greater than about 0.1 percent by weight of the total metal in the coating. Larger amounts such as 5 percent can be used, however, addition of large amounts of silver add to the cost of the coating without deriving corresponding benefits, therefore, when silver addition is used the amounts will generally be from about 1 percent to about 3 percent by weight of the total amount of powdered metal in the coating composition.

To more fully illustrate certain aspects of this invention, the following detailed examples are given. All parts, proportions and percentages are by weight unless designated otherwise.

EXAMPLE I A slurry is prepared by mixing about 80 parts of titanium carbide having essentially all of its particles smaller than the opening in a 325 mesh screen (U.S Sieve) and about 20 parts of a finely divided nickel base alloy (Ni-6.5Cr-4,5Si-3B) with about 40 parts of a nitrocellulose binder such as L-l8 lacquer from Raffi and Swanson and about 40 parts of acetone as a solvent for about minutes in a standard paint type mixer.

The slurry is applied to a clean surface of 410 stainless steel type alloy by spraying with a conventional paint sprayer. Sufficient slurry is used to yield a thickness of about 3 to 4 mils after the coating is air dried to remove most of the solvent. After air drying, the coated article is heated by radiant heating in a furnace at 1,850F in a vacuum for about 15 minutes.

After the material is cooled to room temperature, it is sealed in Visten plastic film bags manufactured by Union Carbide and hydrostatically pressed at a pres sure of about 20,000 psi for about 2 minutes.

After the isostatic pressing step the plastic film is removed and a second coating using the same slurry, except that no titanium carbide is used, is applied to yield an overall coating thickness after air drying of about 6-8 mils. Heating at about 1,850F for about 15 to 30 minutes produces a composite having a 41088 substrate coated with a metal composition containing about 27 percent titanium carbide, about 4.8 percent chromium, about 3.3 percent silicon, about 2.2 percent boron and about 62.7 percent nickel.

Samples of the composite prepared above and uncoated 41058 are tested for erosion by using a conventional grit blaster, using Pangborn 6120 iron grit at 40 psi feed pressure and at a nozzle distance of 5 inches. Results of the erosion tests are given in Table 1 below.

TABLE I loss (inches) The above tests illustrate the superiority of erosion resistant of the composite of this invention as compared to uncoated 410SS.

EXAMPLE ll Using a process substantially similar to that employed in Example I, substrates of lN-7l8 and AM-350 are coated and tested as in Example I, for 5 minutes of erosion. Results of the erosion tests are as follows:

TABLE 11 LOSS (mils) Coated composite Uncoated IN 718 2.1 10 AM 350 1.2 10

The above results indicate the appreciable protection given by the coating compositions of the present invention. Similar results are achieved when the amounts of titanium carbide are varied within the limits disclosed. While there has been shown and described what is at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

1 claim: 1. A process for producing an erosion and wear resis tant metal composite comprising:

a. applying to a clean alloy substrate a first coating of a slurry comprising a powdered metal material, a fugitive organic binder and a volatile solvent for said binder, the metal material consisting essentially of the following weight percentages of ingredients:

nickel 6.5% to 30% chromium 0.5% to 3.5% boron 0.2% to 2.0% silicon 0.3% to 2.5% titanium carbide 67% to 91% b. drying said coated substrate; 0. heating the coated material under an inert atmosphere from about 1,750F to 1,900F for at least about 10 minutes;

d. isostatically pressing said coated material by subjecting said material to pressures of from about 10,000 psi to about 40,000 psi;

e. applying to said coated material a second coating of a slurry comprising a second powdered metal material, a fugitive organic binder and a volatile solvent for said binder, said second powdered metal material consisting essentially of the following weight percentages of ingredients:

nickel to chromium 4.6% to 11.5%

boron2.2% to 5.5%

silicon 3.2% to 8.0%

f. drying said coated substrate; and

g. heating the coated material under an inert atmosphere to at least about 1,780F to about 1,900F for at least about minutes.

2. A process according to claim 1 wherein the weight ratio of titanium carbide to the other metal components in the first slurry is from about 4:1 to about 6:1.

3. A process according to claim 2 wherein the weight UNITED STATES PATENT @FFICE CERTIFECATE 0F CGRECTEQN Patent No. 3. 754,968 Dated Auqust 28, 1973 Inv Barry David Rnvn-ik It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 1, after "producing" cancel "errosion" and substitute erosion Column l, line 21, after"titanium" cancel "carbidc" and substitute carbide Column 1, line 24, after "the" cancel "erison" and substitute erosion-.

Column 1, line 25, after "among" cancel "erosion" and substitute which Column 2, line 17, after "present" cancel"'inventions" and substitute invention Column 3, line 1, after "metal" cancel "power" and substitute powder Column 3, line 1, after "in" cancel "he" and substitute the.

Column 4, line 5, after "first" cancel "and" and substitute Column 6, line 51, after "substrate" "cY' should be on a new line.

r 1 On the cover sheet SLJ "brrosion" should read Erosion Signed and sealed this 26th day of March 197b,.

(SEAL) Attest:

EDWARD PLFLETCHERJR. C. MARSHALL DANN Attesting Officer Commissioner of Patents ORM po'wso (169) USCOMM-DC 60376-P69 9 U5. GOVERNMENT PRINTING OFFICE I969 0-366-334. 

2. A process according to claim 1 wherein the weight ratio of titanium carbide to the other metal components in the first slurry is from about 4:1 to about 6:1.
 3. A process according to claim 2 wherein the weight ratio of said first coating to said second coating is from about 1:5 to about 5:1.
 4. A process according to claim 2 wherein said heating temperatures are from about 1,830*F to about 1,850*F. 